Shortest path bridging (SPB) is an Ethernet standard defined by Institute of Electrical and Electronics Engineers (IEEE) 802.1aq.
Shortest path bridging Mac-in-Mac mode (SPBM) is a mode of the SPB. In an SPBM network, a backbone network includes devices such as a backbone edge bridge (BEB), a backbone core bridge (BCB) and backbone lines connecting these devices.
In the SPBM network, after receiving an Ethernet packet via a user-side interface connecting with a user network, the BEB device searches a media access control (MAC) forwarding table for a matching item according to a target C-MAC address (the C-MAC address is a MAC address of a host in a remote user network) in the Ethernet packet. In the matching item searched out, an out-port is an SPBM tunnel port. The BEB device performs an M-in-M encapsulation of the Ethernet packet according to information included in the SPBM tunnel port to obtain an M-in-M packet, and then forwards the M-in-M packet via a physical out-port.